Technical Abstract:
There is a pressing need for rapid, inexpensive assays which can identify food-and water-borne pathogenic bacteria. Ideally, these assays should consistently detect the presence of pathogens in samples (low false negative rate), while simultaneously not being “fooled” by detecting closely related non-pathogenic or low virulence strains (low false positive rate). This is a particular challenge for enterohemorrhagic E. coli (EHEC), because virulence is dependent on the presence of several different genes, and these genes originate from different sources. For example, one set of critical virulence genes for EHEC are stx1 and/or stx 2, which encode protein Shiga toxins. These genes are contained on lysogenic phages which are capable of transferring the genes between E. coli strains. By comparison, the genes responsible for attachment of EHEC cells to the intestinal lining are part of a pathogenicicity island referred to as the Locus of Enterocyte Effacement (LEE). The LEE is not as readily transmissible between strains as the stx genes but is already very widespread among E. coli strains. Finally, the hemolysin gene is located on a plasmid that can be transmitted between strains. Each of these genes is fairly widespread in the environment and exists in independent populations. Hence, the detection of one or more genes in a sample (water, soil, manure, produce) is at best, only presumptive evidence of the presence of EHEC. Currently, the only definitive evidence is characterization of individual isolated strains.